This application claims the priority of German Application No. 197 49 086.7, filed Nov. 6, 1997, the disclosure of which is expressly incorporated by reference herein.
The invention relates to a device for acquiring data indicative of the path of a lane, such as a road for example, and, more particularly, to a device including a lane detection sensing circuit that supplies lane detection measurement data, an object-positioning sensing circuit which detects at least the distance of an object located ahead of the vehicle and its directional angle relative to the direction of movement of the vehicle, and a vehicle intrinsic movement sensing circuit for detecting movement of the vehicle.
This device includes, first of all, a lane recognition sensing circuit that scans the lane area in front of the vehicle. The sensing circuit supplies lane recognition measurement data, in the form of lane marking coordinates for example. Sensing circuits of this kind are known, for example, in the form of optical lane recognition devices that include an imaging system and an image processing system connected downstream thereof, as disclosed for example in patent documents DE 43 32 836 C1 and EP 0 446 903 B1, as well as DE 42 21 015 A1. They are used in particular for automatic control of the lengthwise and/or transverse movement of vehicles as part of a spacing control device and/or an automatic vehicle steering system. The maximum distance at which lane markings can still be reliably detected by such sensing circuits, i.e. their range, is limited by many factors, such as the installation height of an associated video camera in the vehicle, the weather conditions, the time of day, the degree of contamination of the lane, etc. If the range is too short, autonomous vehicle guidance using these systems alone is no longer reliably possible. Pure spacing regulation devices likewise require knowledge of the lane path at a greater distance, for example up to at least approximately 150 m, with sufficiently high accuracy. Extrapolation of the lane path at this distance from the path recognized by purely optical lane recognition in the near field has proven to be unsatisfactory, at least with low visibility.
On the other hand, the device also includes an object position sensing circuit which detects at least the distance of an object located in front of the vehicle, for example a leading vehicle or an object that is stationary at the edge of the lane, as well as the angle at which this object appears relative to the direction of motion of the vehicle itself. Such sensing circuits are used in particular in spacing regulation devices in order to maintain a constant distance from a leading vehicle. The techniques used for this purpose, such as spacing detection using laser or radar beams, have the advantage that they supply reliable measurement results at greater distances even when optical visibility is low. However, these measurement data alone do not allow determination of the path of the lane.
Devices for acquiring data of a lane path of the type described above have already been proposed in which an object position sensing circuit based on radar is provided for detecting leading vehicles and an optical imaging and image processing system is provided as support for this vehicle-tracking radar in order to estimate the positions of objects ahead of the vehicle itself as an aid to the radar system. However, if the optical system does not supply reliable position data because of poor visibility for example, the performance of the entire system is again reduced to that of the radar system.
It is known that estimating devices in the form of so-called observers or Kalman filters can be used in vehicular applications for calculating certain vehicle-related parameters, for example the directional angle and other values related to driving dynamics. See for example German patent document DE 196 07 429 A1 and the literature cited therein regarding this use of estimation and/or observation concepts in vehicle systems.
The technical problem addressed by the invention is the provision of a device of the above-mentioned type with which lane path indicative data can be acquired comparatively reliably in real-time even under unfavorable environmental conditions. The device must allow, in particular, a reliable acquisition of the lane curvature and/or the transverse position of objects in front of the vehicle relative to the lane.
The present invention solves this problem by providing a device for acquiring data indicative of the path of a lane detection sensing circuit that supplies lane detection measurement data, an object-positioning sensing circuit which detects at least a distance of an object located ahead of the vehicle and its directional angle relative to a direction of movement of the vehicle, and a vehicle intrinsic movement sensing circuit for detecting movement of the vehicle. This device includes an estimating device to which the lane recognition measurement data from the optical lane recognition sensing circuit and the object position measurement data from the object position sensing circuit are supplied. As a function of these measurement data, the device according to the invention determines the lane curvature and/or the positions relative to the lane of any objects detected in front of the vehicle by estimation using an estimation algorithm that can be specified in advance and that incorporates a dynamic vehicle movement model.
In particular, the estimating device can be a so-called observer or Kalman filter. Since the output signals of both the lane recognition sensing circuit and the object position sensing circuit are fed to the estimating device, a non-trivial fusion of both sensor functionalities by the estimating algorithm is achieved in the device. This means that even in the event of a temporary failure of one sensing circuit or the other, a reliable estimate of the lane path and/or the transverse positions of objects in front of the vehicle itself relative to a lane is possible, with the accuracy generally being significantly higher than in the case of a simple provision of both sensing circuits without a sensor-merging estimating device.
In a device according to a preferred embodiment of the invention the geometric relationships between the measured values detected by the lane recognition sensing circuit and the object position sensing circuit are used as the measurement equations and their dynamic relationships are incorporated as state value differential equations into the estimation algorithm. The transverse position of an object detected in front of the vehicle is entered into the differential equation system relative to the lane as a time-constant state variable. This model is especially suitable in embodiments in which the object position sensing circuit supplies the directional angle and the distance of the objects directly and not merely raw data relative to the latter, so that the assignments of the objects relative to the object states and their corresponding measurement equations is provided directly. If this is not the case, an advantageous improvement according to the invention also includes the object distance and its rate of change as state variables in the differential equation system, with the distance change rate being treated as a parameter that is constant over time.
In another preferred embodiment of the invention, the estimating device consists of a Kalman filter.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.